BACKGROUND AND OBJECTIVE: The serum paraoxonase and arylesterase activities are related to coronary artery diseases. However, there are a few data about the association of paraoxonase and arylesterase activities with in-stent restenosis (ISR). The aim of this study was to evaluate the relationship between paraoxonase and arylesterase activities and ISR in patients with bare metal stent (BMS). MATERIALS AND METHODS: Thirty-one patients with normal coronary artery (group 1) and 60 with BMS were enrolled in this observational study. According to the ISR, the patients were classified as group 2, without the ISR (n=29) and group 3, with the ISR (n=31). Serum paraoxonase and arylesterase activities were measured spectrophotometrically. RESULTS: The paraoxonase and arylesterase activities were lower in patients with BMS than in the individuals with normal coronary artery (P<0.001 and P=0.001, respectively). The enzyme activities were also higher in patients without ISR than with ISR (both of P<0.001). In bivariate correlation analyses in patients with BMS, ISR shows significant positive correlations with the presence of hypertension and hyperlipidemia, type C lesion, and stent length, but shows negative correlations with type A lesion stent diameter, high-density lipoprotein cholesterol, and paraoxonase and arylesterase activities. In regression analysis, ISR is independently associated with paraoxonase and arylesterase activities (β=-0.216, P=0.038 and β=-0.452, P<0.001, respectively), type A lesion (β=-0.251, P=0.013), and stent diameter (β=-0.192, P=0.024) in patients with BMS. CONCLUSION: Our study shows that decreased paraoxonase and arylesterase activities play a significant role in ethiopathogenesis ISR in patients with BMS.